1. Field of the Invention
This present invention relates to a sheet processing apparatus, and more specifically to a sheet processing apparatus having a feeding structure which improves the stability of sheet feeding and reduces the manufacture cost, and a sheet processing method.
2. The Related Art
Please refer to FIG. 1, a conventional sheet processing apparatus 100′ comprises a sheet-conveying mechanism and an image-forming mechanism 5′. The sheet-conveying mechanism has a stacking plate 1′ for holding sheets of paper 8′, a sheet-separating unit 2′, a convey unit 3′, a discharge unit 6′ and a discharge tray 7′ for receiving the scanned sheets of paper 8′. The sheet-separating unit 2′ includes a sheet-separating roller 21′ and a retard pad 22′ disposed above the sheet-separating roller 21′, with a convey path formed therebetween. A pick spring 11′ is arranged above the stacking plate 1′ and adjacent to the retard pad 22′ for pressing the sheets of the paper 8′. The sheet processing apparatus 100′ further has a sensor 41′ mounted to a bottom of the stacking plate 1′, with a sensor arm swinging upwards for detecting whether there is any sheet of the paper 8′ settled on the stacking plate 1′, and a sensor 42′ with a sensor arm, disposed between the sheet-separating unit 2′ and the convey unit 3′ for detecting whether one sheet of paper 8′ passes therethrough.
When the sheet processing apparatus 100′ is in work, the sheets of paper 8′ are put on the stacking plate 1′, pressing the sensor arm of the sensor 41′ downwards. The sheet-separating roller 21′ has a frictional outer peripheral surface to feed a lowermost sheet of paper 8′ forwards, cooperating with the retard pad 22′. The lowermost sheet, designated 81′, is conveyed forwards with a linear speed V1 before caught by a convey roller 31′ of the convey unit 3′. The sensor arm of the sensor 42′ is pushed upwards by the moving sheet 81′ to generate a signal sent to a system controller. The image-forming mechanism 5′ is commanded accordingly by the system controller to start scanning at a proper time. The outer peripheral linear speed of the convey roller 31′ and a discharge roller 61′ of the discharge unit 6′ are V2, correspondingly, when the sheet 81′ is conveyed forward by the convey unit 3′, it is moving at the linear speed V2 because the force acted on the sheet 81′ from the convey unit 3′ is greater than that from the sheet-separating unit 2′, until the sheet 81′ is received in the discharge tray 7′. During this period, when the sheet 81′ leaves off the sheet-separating unit 2′, a sheet above the sheet 81′, designated 82′, comes into contact the sheet-separating roller 21′ and is urged to move forward at the linear speed V1. Since the linear speed V2 is faster than the linear speed V1, the sheet 82′ is spaced away from the sheet 81′ with an increasing gap formed between the two adjacent sheets of paper. As a result, when the sheet 81′ is apart from the sensor 42′, the sensor arm of the sensor 42′ returns the original position before being pushed upward by the subsequent sheet 82′, and generates another signal sent to the system controller. The image-forming mechanism 5′ is commanded by the system controller to stop scanning of sheet 81′ at a proper time. The image-forming mechanism 5′ is controlled to set the start time and the end time of scanning each sheet according to the two different signals caused by the gaps between the sheets of paper, thereby obtaining the scanned images of each sheet of paper.
However, since the linear speed V2 is faster than the linear speed V1, the convey roller 31′ will pull and drag the sheet of paper which is partly restrained between the sheet-separating roller 21′ and the retard pad 22′, which will affect the conveying stability of the sheets of paper, or even damage the sheets of paper. Consequently, it affects the quality of the scanned image. Furthermore, the convey roller 31′ is applied with a backward pulling force from the sheet-separating unit 2′ via the sheet of paper, which increases the load of the stepping motor which drives the convey roller 31′, and influences the processing efficiency of the sheet processing apparatus 100′.